Comparison of charge injection in SOI and bulk MOS analog switches

Abstract

Summary form only given. The analog MOS switch is one of the major building blocks in switched-data circuits (switched capacitor, current-copier, track-and-hold, etc.). Their main limitation regarding accuracy is linked to the problem of charge injection that induces output voltage errors. Several physical studies recently addressed the charge injection problem in bulk MOSFETs under low-voltage conditions (considering the weak inversion contribution) or in SOI MOSFETs under large voltage transients. In this paper we compare charge injection in bulk and SOI MOS switches from a low-voltage circuit point of view, using MEDICI 2-D simulations, for three different MOS processes: typical bulk with a threshold voltage (VT) of 0.72 V, comparable fully-depleted SOI with VT=0.74 V, and low-voltage SOI. Our analysis has demonstrated significant differences in the charge components injected by bulk and SOI MOS switches and their dependence on process and circuit conditions. In carefully optimized circuits, low-voltage fully depleted SOI MOS switches may inject much less charges than in bulk and enable better compensation results.